Tube Tech has developed a robotic fired heater convection bank cleaning technology (shown in Figure 4) to specifically address the issue of poor or limited access encountered when attempting to remove fouling from the convection banks of fired heaters.

The robot acts as a delivery vehicle for one or two lances, capable of delivering the range

of cleaning media shown in Table 1. The choice of cleaning medium (see Table 1) is dependent on the nature of the deposit. The blast medium cleaning radius is delivered within a distance of one inch from the fouled surface.

As a consequence, the robot can remove the hardest of deposits and can do so between every tube row while providing 360 degree tube surface contact, regardless of whether the design is square or triangular pitch.

The robot can either use one lance for cleaning and one for inspection – allowing

inspection to follow immediately after to verify cleanliness without delay, conversely two lances can be used for cleaning, resulting in twice the productivity per robot. Productivity can be further enhanced and downtime reduced further by the simultaneous deployment of multiple robots, at multiple levels.

The robotic cleaning procedure begins with the placing of the robot on top of each

convection bank via existing access doors. If new doors are required, they can be cut in whilst the furnace is running prior to shut down, thereby removing this element from the shut down period, reducing down time further. The door size can be as little as 150 mm x 200mm in dimension and as large as 24 in².

The robot is equipped with cameras allowing it to be remotely controlled from an operator

external to the convection bank in which the robot has been placed. The lances are remotely

activated and are preset to the technical drawings provided by the client, ensuring that each

row of each convection bank is cleaned at every level (see Figure 5). The robot can negotiate a convection bank with as many as 20 rows from top to bottom. It can also operate

vertically upwards.

Once cleaning has been completed, the robot inspects between each row with a flat,

blade shaped camera and records the data for cleanliness, and integrity evaluation whereby

images and video clips are recorded for archive purposes. The resulting archives can be used

by clients to be used as a benchmark, for post contract evidence and for future cleaning and

inspection assessments which can be matched to overall fired heater performance before and after future cleaning exercises.

Figure 5. Images showing the manner in which the robot can access deep between

every tube row for the very first time regardless of depth.

Regardless of whether the convection bank is square pitch or triangular pitch, the blast

cleaning pressure emitted from the nozzles does not hit the refractory as the angle of the jets

is such that they deflect off the tubes first where the pressure is dissipated quickly. There is

therefore no danger of refractory damage, as witnessed by Shell Global Solutions, worldwide

independent consultants.

The refractory will only ever get damp and the moisture is easily evaporated during the normal run up procedures. A shroud can be easily attached to the lance to provide plant operators with extra confidence that the high pressure blast medium such as liquid ice, CO2, water, etc., does not make contact with the refractory wall.

The robot delivers any cleaning medium e.g. air, steam or water at pressures ranging

from 600 psi to 60,000 psi (4000 bar) with volumes as low as 2.5 litres per minute and can be collected below the last convection bank and removed to an awaiting tanker or straight to the plant’s interceptor tank.

The development of robotic cleaning systems means that fired heater operators now have

the choice between either manual or static lancing (both of which in many cases struggle to

remove the more tenacious and fused deposits) or robotic fired heater convection section

cleaning which ensures removal of any form of deposit no matter how hard delivering a far

superior clean combined with inspection within a window of just two days. This is made possible by the way the robot runs up, down and across every row and physically penetrates every deposit across every tube row.

As the rate of deposit formation is often dependent on surface roughness, with rough

areas providing nucleation sites for new deposits (9), the better the finish on the finned

convection bank tubes, the slower the fired heater’s performance will degrade, allowing the

operator to delay the unit’s next clean for longer.

When selecting the cleaning method for a fired heater’s convection bank – it is crucial to

consider the risk of cleaning failure, which is particularly high when the fouling is in the form of harder deposits. Should a standard lancing technique fail, the operator will be forced to take the unit offline sooner, adding lost production to the cost of cleaning.

Robotic fired heater convection section cleaning is extremely cost effective considering the improvement from an average of 2% surface coverage to near 100% surface area coverage.